CCD (Charge Coupled Device) sensors and CMOS (Complementary Metal Oxide Semiconductor) sensors are types of 2-dimensional sensors for photographing moving pictures and stationary pictures and main elements in the configuration of electronic cameras. Specifically, the CCD sensors show more excellent characteristics in picture quality than the CMOS sensors, but, because of its power consumption and complex configuration, the market share of the CMOS sensors is becoming higher, and, currently, the picture quality of the CMOS sensors is improving. As these sensors become developed, the uses of digital cameras are becoming universal, and cameras are being installed on mobile phones such as cellular phones.
Typical camera modules employ VCM (Voice Coil Motor) for automatic focus drivers as disclosed in KR 2013-0035522.
The VCM includes a barrel configured by a coil and a magnet and including multiple lenses, in which the barrel is supported by springs disposed at upper and lower parts of the barrel. The springs disposed at the upper and lower parts guide the linear motion of the driver, and when the VCM is not operated, return the lens barrel to the initial position.
The operating principle of the VCM is as follows.
The VCM is driven in the optical axis direction of the lens by Lorentz force generated when current flows through the coil in a magnetic field formed by the magnet. The VCM transforms electrical energy to mechanical energy by the generated force.
Currently, as mobile phones and mobile electronic devices require light weight, small size, thin thickness and low power consumption, camera modules installed in these products also require low power consumption and size reduction. Accordingly, there are needs for low power/size reduction for the automatic focus device provided in the camera module.
However, the automatic focus device used in typical mobile phones needs to drive the barrel including the lenses by a VCM scheme, so large power consumption is required. In addition, because the coil and magnet positioned near the barrel are used to drive the barrel in a direction vertical to the optical axis, size reduction is difficult. Thus, a new automatic focus device is in demand.